Much attention has been directed for many years to the design of reduced pressure patient support systems for maximizing patient comfort and reducing the complications of pressure sores in bedridden patients. One of the early widely used therapies in this field was a floatation system marketed under the trademark "CLINATRON." This device is a large tub containing an air permeable sack filled with micron-sized silicon spheres. The spheres are formed into a fluidized bed by massive introduction of air into the sack. This device marked the early stages of hospital rental equipment for patients at risk because of skin grafts, burns or pressure sores. The equipment was bulky and weighed almost one thousand pounds. An extremely large blower was required to effectuate the system, and any tears in the sack containing the silicon spheres could cause spheres to be blown out around the area of the apparatus. Despite its problems, and the great expense associated with utilization of the equipment, it has been widely used for patients at risk from excessive bed pressure.
In more recent years, a class of devices has been introduced which the industry has come to designate as "low air loss". A typical low air loss support system has a plurality of upstanding parallel vapor-permeable air sacks inflated to provide support for the patient. Such devices are marketed under the trademarks "Monarch,""Air Plus," "Flexicair," and "Kin Air". The approach of this class of equipment is to provide gradual leakage of air from the sacks, either by perforating them at selected locations or by providing a "breathable" sack material which is permeable to the passage of vapor. Typically, air is pumped from a manifold on one side of the bed through the sacks extending transversely of the bed. The air is wholly or partially exhausted through holes or pores in the sacks and at least in some instances, through an exhaust port. The air losses necessitate the use of a rather large air pump or blower, and the systems constructed of this type tend to be bulky and expensive. To seek to avoid infection problems stemming from the holes or open pores of the sack material, special sterilization precautions are necessary. The beds are not easily adaptable to ordinary hospital use and are not radiolucent so as to permit taking X-rays of a patient lying in one. This class of beds includes electrical circuitry making its use unacceptable in certain hospital environments. Because of their air loss characteristic, these beds cannot support the patient when blower operation is terminated. Thus, if the patient is to be transported to another hospital area, the sacks will be deflated unless battery power backup is provided. Despite their deficiencies, these beds have grown to dominate the market, which is predominantly served by the temporary leasing of these special purpose beds to hospitals as required for particular patients, generally at a rate to the hospital of about $100.00 per day. For reference, U.S. patents issued to makers of such commercial beds include U.S. Pat. Nos. 3,822,425, 3,909,858, 4,099,276, 4,488,322, 4,525,585 and 4,638,519.
Other simple approaches to providing reduced pressure patient support systems include water mattresses, air mattresses (including types with varying air pressure in alternating sections of the mattress) and egg-crate mattresses.
The utilization of the present invention is believed to present a substantial advance over the technology known in this industry. By providing an essentially zero air-loss system adapted to permit the clinician to carefully and quickly control the air pressure in all parts of the support system and to quickly carry out procedures required for care of the patient, the invention overcomes many of the problems of the art. The air sacks and electrical components of the system can quickly be installed or removed from a radiolucent intensive care bed. On removal, there are no electrical components remaining on the bed, and the bed may be utilized efficiently in ordinary hospital use. Because the invention does not utilize air sacks with holes or permeable pores, problems of infection and sterilization are minimized. The no-air loss approach permits the utilization of a much more compact air flow source. The end result is a system which is lightweight and relatively simple and inexpensive. The bed may be transported without air pump operation while still maintaining air pressure in the sacks to support the patient. The system is readily adaptable to automatic, time-varying rhythmic pressure variance therapies. It also may be adapted to automatic pressure control in feed back loops responsive to the weight and position of a patient.